Air bypass for free piston engine



May 3, 1960 slMoN K. CHEN 2,935,056

AIR BYPASS FOR FREE PISTON ENGINE Filed March 7, 1958 2 Sheets-Sheet l kg V May 3, 1960 SIMON K. CHEN 2,935,056

AIR BYPASS FOR FREE PISTON ENGINE Filed March 7, 1958 y2 Sheets-Sheet 2 l IN1/EWE 6h/ONK C21/EN fmfA/Ey "it, ...n

`AIR BYPASS FR FREE PISTON ENGINE Application March 7, 1953, Serial No. 719,869

s claims. (ci. 12s- 46) This invention relates to a free piston engine. More specifically the engine relates to an improved bypass mechanism for free piston engines.

A free piston engine of conventional design generally includes a compressed air chamber also conventionally referred to as an air box. During the operation of the free piston engine compressed air is stored within the compressed air chamber and this air during a certain position of the pistons serves to scavenge the combustion chamber whereupon the said air and exhaust gases are directed to an exhaust collector which in turn may be in communication with a gas turbine. In a free piston engine, only a part of the compressed air is retained in the power cylinder or combustion chamber for the purposes of combustion. Air which is not trapped in the power cylinder is generally called blow-through-air. At peak design load, this air serves to cool the power cylinder and is absolutely necessary. At part loads, however, the average power cylinder gaseous temperature'is considerably lower and cooling therefore is not as criticall as it is at peak design loads. Therefore, during load conditions less than peak loads, a large portion of the so-called blow-through-air is not needed within the combustion cylinder and therefore may bypass directly through the exhaust collector by means of a suitable mechanism which comprises the prime object of this invention. Thus, broadly, it is a prime object of this invention to provide means whereby air from the compressed air chamber may be directed through a bypass separate of the combustion chamber during certain operating con-l ditions of a free piston engine.

It is another object of this invention to provide an irnproved bypass means for the compressed air chamber of a free piston engine whereby the overall pressure drop within the power cylinder can be reduced since all of the air is not passing through the inlet port of the combustion chamber during certain part load operating conditions. It is a further object of the present invention to provide an improved bypass mechanism for bypassing air from the compressed air chamber of a free piston engine directly to the exhaust collector whereby the overall pressure drop can be reduced and therefore at minimum operating loads, such as in idling, a more economical part load operation will result.

A specific object is the provision of an improved bypass mechanism for bypassing air from the compressed air chamber of a free piston engine directly to an exhaust collector during certain operating conditions of the engine, the said bypass mechanism including a valve automatically controllable by the compressed air chamber pressure.

A further object of the invention is to provide an imamined in connection with the accompanying sheets of drawings. 4

Figure 1 is a cross sectional view through a free piston engine showing an improved bypass mechanism for bypassing compressed air from a compressed air chamber;

Figure 2 is an enlarged cross sectional detail view of a bypass mechanism for a free piston engine;

Figure .3 is a cross sectional view taken substantially along the line 3-3 of Figure 2;

Figure 4 is an enlarged cross sectional view showing a bypass mechanism for the compressed air chamber of a free piston engine, the said mechanism being a modified type;

Figure 5 is a fragmentary cross sectional view of the modified form of bypass mechanism shown in Figure 4,

the said view showing another operating position of the mechanism;v and Figure 6 is a cross sectional view taken substantially along the line 6 6 of Figure 4.

Referring now particularly to Figures l through 3, a free piston engine is generally designated by the reference character 10. The free piston engine 10 comprises a casing 11 having an outer cylindrical wall 12 which encloses a cylinder 13 having a centrally disposed combustion chamber 14. The combustion chamber 14 has positioned therein'for reciprocation a pair of opposed power pistons 15 which at their opposite ends are connected to compressor pistonsl. Each compressor piston 16 is movable with each power piston 15, the said compressor pistons 16 being disposed for reciprocation within bounce chamber 17 disposed at opposite ends of the casing 11. Each bounce chamber 17 is formed by a cylindrical wall 18 suitably positioned within the casing 11. A divider Wall 19 separates each bounce chamber 17 from a com pressed air chamber 20 formed within the casing 11. The outer cylindrical wall 12 is formed -with suitable inlet openings 21 which are in direct communication with the atmosphere.

The divider walls `19 include a plurality of valves 22 (only one of which is shown for each divider wall 19) the said valves 22 opening inwardly into the compressed air chamber 20. Each cylindrical wall includes a plurality of lvalves 23 which open inwardly into each bounce cham- The cylinder 13 is provided with a plurality of scavenging openings 24 which provide for the inlet of air into the combustion chamber 14 from the compressed air chamber 20.

An exhaust collector 25 is in communication with the combustion chamber 14 by means of an opening 26 in the cylinder 13. A suitable rack and pinion arrangementv 27 is provided for synchronizing the reciprocation ofthe power piston 15. This arrangement is conventional and need not further be described. A conventional fuel injection nozzle 28 is suitably supported on the casing .11 for injecting fuel into the combustion chamber 14.

Referring again to Figures l through 3, a compressed air bypass mechanism is indicated by the reference character 30. The bypass mechanism 30 comprises a wal-l 31 of the exhaust collector 25, said wall including an opening or port 32. A valve support 33 is positioned within the compressed air chamber 20, the said valve support V33 comprising a rectangular aperture 24 adapted 'to cornmunicate with the port 32. The valve support 33 further includes a vertical slot 35 having at its upper end avrelief bore 36 which communicates directly with the compressed air chamber 20. A valve 37 is positioned for opening andV closing the apertures 34, the said valve 37 being adapted to engage a valve seat 38 for closing the port 32. The valve 37 includes a guide 39 which is adaptedto cent'ei" and reciprocate in the upper portion of the vertical'islot 35. A 'stem 40 is connected to the valves 37, the said stem'being adapted to reciprocate in the vertical slot 35. A cylinder 41 is formed in the valve support 33, the said cylinder having its lower open end in communication with the compressed air chamber 20. A piston 42 is reciprocably positioned within `the cylinder 41, the said piston having its lowermost surface in direct communication with the compressed air chamber 2G. An O-ring 43 is supported on the piston 42 for suitably sealing the compressed air chamber 20 from the portion of the cylinder 41 above the piston 42. The piston d2 is suitably connected to the stem 40 by means of the securing member or bolt 44. A spring 45 is positioned within the cylinder 41 for normally urging the piston 42 outwardly to .normally maintain the valve 37 in an open position. A port 46 on the valve support 43 communicates with the bore 47 in communication with the atmosphere.

I n the operation now, assuming that the free Vpiston Aengine is operatingat a peak design load, the compressed airwithin the compressed air chamber 2t), upon the outward movement of the pistons 15, flows into the combustion chamber 14 for scavenging the same through the exhaust collector 25. At this design or peak load itis desired to utilize as much air as possible to achieve suitable scavenging and also to suitably cool the cylinders 13. However, as the load is reduced, it is not necessary to provide as large a volume of air for scavenging and cooling purposes. During the peak load condition, it is desired that the port 32 be closed so that the bypass mechanism is ineffective and the total volume of air flows through the combustion chamber 14 into 'the exhaust collector 25. in view of the pressure within the compressed air chamber 20, the pressure is sutiicient to force the piston 42 upwardly whereupon the valve 40 closes the `port 32 since the compressed air pressure overcomes the action 'of the spring 45 and keeps the valve 40 in the closed position. At the load now descreases, the pistons are not forced outwardly to as great an extent since the inflow of fuel through the fuel nozzle is curtailed and less air is required in the combustion chamber i4. Thus a pressure drop occurs which results in the spring 45 exerting sul'licient force on the piston 42 to overcome the pressure in the compressed air chamber 20 whereupon the valve 37 is moved downwardly into the position shown in Figure 2 and bypass of air can occur from the compressed air chamber 20 through the exhaust collector 25 and to the gas turbine. The volume of air bypassed, of course, is also dependent upon the exact position of the valve 37 which may be calibrated .as to be directly responsive in relation to the compressed air pressure whereupon more or less of the valve closes the port 32 so that a regulation of the port 32 is obtained. Thus in the low operating part load condition of the free piston engine, bypass of the compressed air is permitted into the exhaust collector 25. It is thus apparent that the compressed air mechanism 30 is directly responsive to the air pressure within the compressed air chamber Z0. Thus the overall pressure drop can be reduced since not all of the airis passing through the inlet port into the combustion chamber 14 during the 'part load operation of the engine. Furthermore, less air is passing into the combustion chamber during a condition where less air is required and less cooling of the cylinder is necessary. Thus, a greater vefficiency in the operation results. It is thus obvious that the objects of the invention have been achieved.

Referring now particularly to Figure 5, a modied type of bypass mechanism is disclosed, the said mechanism 'being .generally designated -by the reference vcharacter 50. .All other portions of the free piston engine remain the same andthu's thereference characters applied to Vthe free Cil and the compressed air chamber 20. A valve seat support 52 is positioned within the compressed air chamber 20 adjacent the opening 51, the said seat support comprising a valve seat 53. A valve 54 is adapted to open and close the opening 51 by means of its association with the valve seat 53. A pair of laterally spaced projections 55 extend vinwardly from the wall 31, the said projections comprising supporting means for a shaft 56. The shaft 56 extends through a bore 57 Yand is suitably connected to the said valve 54 so that upon movement of the valve 54 the said shaft 56 rotates on the projections 55. The valve 54 includes an arm 58 having a link 59 connected thereto by means of pivotal connection means 60. The link 59 projects outwardly through the casing 11 and may be suitably connected to a manual control or also may be suitably connected to an automatic control means not shown), the said control means cooperating with operating controls such as the fuel control of a free piston engine or other control means related to a gas turbine. A spring retained plate 61 is connected to the link 59, the retainer plate 61 including ka spring 62 which is adapted to normally .retain the valve 54 in the closed position shown in Figure 4. As shown in Figure 5, movement of the link 59 serves to pivot the valve S4 to the open position. l

The bypass mechanism 50 is operable under similar operating conditions as described above in connection with the bypass mechanism 30. During peak operating conditions, the valve 54 is maintained in the closed position shown in Figure 4 and during part load operating conditions the valve 54 may be opened as indicated in Figure 5.

The opening of the valves shown is controlled by the air box or compressed air chamber pressure, though they ,may lsuitably cooperate and be responsive to the exhaust v temperature, or, if desired, with respect to the turbine output of a gas turbine engine. The valves may also be suitably placed into operating connection with the fuel lcontrol valves so that the bypass will be greater when the fuel flow is decreasing as a result of fuel throttle control. As shown in the tirst mentioned embodiment of the invention, the Valve is automatically responsive to the air box pressure and the bypass opening is adjusted accordingly.

Thus it is clearly apparent that the objects of the invention have been fully achieved and it must be understood that changes and modifications in the invention may be made without departing from the spirit of the invention or the scope thereof as dened in the appended claims.

What is claimed is:

l. In a free piston engine having a casing including a combustion cylinder, power pistons reciprocable in said cylinder, .a compressed air chamber adapted to receive air during movement of said power pistons 'in a direction toward each other, said cylinder including an inlet adapted to intermittently connect said compressed air chamber and said cylinder, and an exhaust collector adapted to exhaust said 'combustion cylinder; a compressed air bypass mechanism comprising a portion on said casing having a valve opening adapted to provide communication between said exhaust 'collector and said compressed air chamber, a valve support adjacent said valve opening, a valve element on said support movable to open and close said valve opening, a cylinder on said support, a piston movable within said cylinder in response Vt'o pressure dierentials on opposite sides of said piston, means connecting said piston to said valve element to move the same, biasing means normally urging said piston and valve to an open position relative to said opening during a low pressure within said compressed aid chamber and part load operating condition of said engine whereby air bypasses from said compressed air chamber to said exhaust collector,

vsaid piston being responsive to a high pressure within said compressed 'air `chamber rduring peak load operating condition of said engine to move said valve to a closed posiltion .to close 'said valve openings.

2. In a free piston engine having a casing including a combustion cylinder, power pistons reciprocable in said cylinder, a compressed air chamber adapted to receive air during movement of said power pistons in a direction toward each other, said cylinder including an inlet adapted to intermittently connect said compressed air chamber and said cylinder, and an exhaust collector adapted to exhaust said combustion cylinder; a compressed air r4bypass mechanism comprising a portion on said casing having a valve opening adapted to provide communication between said exhaust collector and said compressed air chamber, a valve element movably supported adjacent said valve opening and adapted to open and close said valve opening, a cylinder adjacent said valve element, a piston movable within said cylinder in response to pressure differentials on opposite sides of said piston, means connecting said piston to said valve element to move the same, biasing means normally urging said piston and valve to an open position relative to said opening during a low pressure within said compressed air chamber and part load operating condition of said engine whereby air bypasses from said compressed air chamber to said exhaust collector, said piston being responsive to a high pressure within said compressed air chamber during peak load operating condition of said engine to move said valve to a closed position to close said valve opening.

3. In a free piston engine having a casing including a combustion cylinder, power pistons reciprocable in said cylinder, a compressed air chamber adapted to receive air during movement of said power pistons in a direction toward each other, said cylinder including an inlet adapted to intermittently connect said compressed air chamber and said cylinder, and an exhaust collector adapted to exhaust said combustion cylinder; a compressed air bypass mechanism comprising a portion on said casing having a valve opening adapted to provide communication between said exhaust collector and said compressed air chamber, a valve element movably supported adjacent said valve opening and adapted to open and close said valve opening, a cylinder adjacent said valve element, said cylinder being in communication with said compressed air chamber, a piston movable within said cylinder in response to pressure diierentials on opposite sides of said piston, means conecting said piston to said valve element to move the same, biasing means normally urging said piston and valve to an open positon relative to said opening during a certain pressure within said compressed air chamber and part load operating condition of said cngine whereby air bypasses from said compressed air chamber to said exhaust collector, said piston being responsive to increased pressure within said compressed air chamber during peak load operating condition of said engine to 6 move said valve to a closed positon to close said valve opening.

4. In a free piston engine having a casing including a combustion cylinder, opposed power pistons reciprocally positioned within said cylinder, a compressed air chamber, said air chamber being adapted to receive air during movement of said pistons in a direction toward each other, said combustion chamber being in intermittent communication with said compressed air chamber, and exhaust means communicating with said combustion cylinder; a compressed air bypass mechanism including a portion of said casing having a port adapted to provide communication between said compressed air chamber and said exhaust means, valve means movably supported on said casing for opening and closing said port, means for moving said valve means comprising a uid pressure responsive element connected to said valve means and communicating with said compressed air chamber, said fluid pressure responsive means being responsive to a lowering of the pressure within the compressed air chamber during part load condition of said engine to move said valve to an open position, said valve being movable to a closed position during an increase in pressure during peak load operating condition of said engine within said compressed air chamber.

5. In a free piston engine having a casing including a combustion cylinder, power pistons mounted for reciprocation within said cylinder, a compressed air chamber adapted to receive air within said chamber during movement of said power pistons in a direction toward each other, said cylinder including an inlet adapted to intermittently connect said compressed air chamber and said cylinder, and an axhaust means adapted to exhaust said combustion cylinder; a bypass mechanism including means on said casing having a port adapted to provide communication between said compressed air chamber and said exhaust means, a valve connected to said valve mechanism adjacent said port for opening and closing said port, a control member connected to said valve for moving the same to open said port during part load operating condition of said engine whereby air from said compressed air chamber may be bypassed directly to said exhaust means during certain operating conditions of the engine and to close said port during peak load operating condi` tion of said engine.

References Cited in the le of this patent UNITED STATES PATENTS 2,162,967 Pescara June 20, 1939 2,200,892 Pescara May 14, 1940 2,435,232 Morain Feb. 3, 1948 

